The present invention relates to an electrical instrument such as a computer apparatus, and the like, and more specifically, to an electrical instrument using a plurality of battery blocks and batteries as a battery, and the like.
In a variety of electrical instruments including information terminal instruments represented by a notebook personal computer (notebook PC), personal instruments such as a PDA (Personal Digital Assistant), various portable audio instruments, video cameras, and the like, there is a case of receiving a supply of electrical power from a battery (storage battery, secondary battery) usable over and over again while repeating charge/discharge, besides a case of receiving the supply of electrical power directly from a commercial power supply through, for example, an AC adapter. As this battery, a nickel-metal hydride battery (NiMH battery) or a nickel-cadmium battery (NiCd battery), which has a relatively large capacity and is inexpensive, is used. Moreover, there is a case where a lithium-ion battery which has a higher energy density per unit weight as compared with the nickel-cadmium battery, a lithium-polymer battery using a solid polymer without using a liquid electrolyte, or the like, is used.
Among the electrical instruments as described above, for example, the notebook PC is configured to be able to be equipped with a battery pack in which such a kind of battery is housed, and a user operates a system body of the notebook PC by battery drive at a place where an AC power supply is not present. However, an operating time of the battery from a full charge state thereof in the battery pack is not always satisfactory to the user. Therefore, a notebook PC having a so-called dual battery system in which two batteries are mounted has been heretofore proposed. Specifically, there has existed a model capable of attaching a battery pack of a second battery, instead of, for example, a drive of a CD-RW, a DVD and the like, to an expansion bay, an expansion base (Ultrabase) or the like, in addition to a battery pack of a main battery (standard battery), which is attached to a cabinet of the system body.
As conventional technologies described in publications, for example, in an apparatus provided with a first battery and a second battery, there has already existed a technology of constantly grasping states of the batteries, activating the batteries, and extending lifetimes thereof in a manner that a load switching circuit is controlled to alternately connect the first battery and the second battery to a load circuit (for example, refer to Patent Document 1). Meanwhile, the inventors of the present invention have already proposed an invention in which, in the apparatus provided with the first battery and the second battery, a loss of electrical power due to a diode is prevented to extend an operating time by battery drive (for example, refer to Patent Document 2).
[Patent Document 1] Japanese Patent Laid-Open No. Hei 8 (1996)-37740 (pp. 3-4, FIG. 1)
[Patent Document 2] Japanese Patent No. 2708374 (pp. 5-7, FIG. 2)
Meanwhile, the inventors of the present invention continue to research a technology of constituting one battery pack by mixing different types of batteries. When different types of battery cells are connected in series or in parallel, in general, the battery cells are rapidly deteriorated. Accordingly, the different types of battery cells are not usually used in a mixed manner. When a plurality of battery cells are used as a block, it is common to form the block while equalizing characteristics of the plurality of battery cells as much as possible. In this case, for example, even if the battery cells are of the same type, and a lot or the like in manufacture thereof is the same, the same ones in performance are further selected for the battery cells. However, for example, even if there is an unused space in the battery pack, the space cannot be completely filled depending on a shape of the cells, and such an empty space has not been able to be utilized effectively. For example, cylindrical and rectangular lithium-ion batteries cannot be mixed even if both of them are equally the lithium-ion batteries. If these batteries can be mixed, it becomes possible to utilize the space effectively, thus making it possible to design a shape of the battery pack flexibly.
Therefore, the inventors of the present invention are pursuing a research on commercialization of a hybrid battery in which cell blocks (battery blocks) are composed by connecting single cell batteries in series or in parallel for each of the battery cells of the same type. In the hybrid battery as described above, in which the plurality of battery blocks are arranged, a configuration in which different cells are not electrically connected to each other is adopted, and thus an occurrence of the cell deterioration is suppressed. However, when the number of charge/discharge cycles is increased in one of the battery blocks significantly more than in the other battery block, a degree of the battery deterioration is increased as the number of charge/discharge cycles in the one battery block is increased. Consequently, a battery lifetime of the hybrid battery is lowered. This hybrid battery forms one cabinet as a battery pack, and the deterioration of the one battery block leads to a deterioration of the entire hybrid battery. As a result of this, a total battery capacity of the hybrid battery is reduced.
Moreover, as described in a column of the Background Art, also in the dual battery system in which the plurality of batteries such as the main battery and the second battery are mounted on the instrument, there is a case where only one of the batteries is preferentially used. In such a case, only the one battery shortens a lifetime thereof extremely, as well as the entire battery capacity is also lowered. For example, in the Patent Document 1, when it is assumed that the first battery is the main battery and the second battery is the second battery (sub-battery connected to the bay drive), in the case of a user usually using the notebook PC without connecting the second battery to the bay drive, only the number of charge/discharge cycles of the main battery is increased. In this case, the problem described above cannot be solved only by performing the alternate switching control as in the Patent Document 1. Meanwhile, for a user who has purchased a new notebook PC, a state where only the number of charge/discharge cycles of the second battery is increased is brought. In this case, only a lifetime of the second battery is extremely shortened only by performing the alternate switching control as in the Patent Document 1.